Geo-characterisation of lime water treatment sludge

In-situ and laboratory tests were performed on lime sludge generated from a drinking water-softening process and disposed of in a sedimentation lagoon. The sludge consists predominantly of calcite. It is poorly graded, lowplasticity silt with in-situ wc around 70%, ft around 15 kN/m3 and e between 1·5 and 2·5. The optimum wc for standard and modified Proctor compaction is 30% and the maximum fd values are 12 and 13·5 kN/m3 respectively. The Cc and Cr for undisturbed sludge specimens are 0·54-0·68 and 0·021-0·046. C_v and k decrease with increasing vertical stress. The disposed sludge is sensitive and the in-situ S_u,max varies with depth. Stratification of the sludge is evident by the varying values of in-situ S_u,max, S_u,r and St with depth and Vs profiles. Potential engineering reuse options for the sludge are buffer for acidic soil and low-permeability fill for landfills and brownfields, as well as engineering fill. The properties of lime sludge are different from those of coagulation sludge, primarily due to their different chemical compositions. Coagulation sludge has the physical characteristics of high-plasticity clay. Consequently, lime sludge shows comparatively higher fd, lower Cc and Cr and higher C_v than coagulation sludge.